1. Field of the Invention
This invention relates to a method for preparing a water-soluble organic silicon compound which is useful as an aqueous agent for preventing water absorption of porous materials and a primer for various paints and finishers.
2. Prior Art
For the purpose of preventing water absorption of porous materials, especially porous building and construction materials, it is a common practice to coat or impregnate porous materials with solutions of silicone, acrylic, urethane, ester and fat resins or monomers followed by drying. Among these, silicone systems are widely used, and water absorption preventing silicone agents of the solvent dilution type constitute the mainstream.
Since the solvent dilution type involves risks of fire, explosion and poisoning, and from the aspects of global environment protection and resource utilization, it is desired to develop a water-absorption preventing agent free of a solvent, especially a high performance aqueous water-absorption preventing agent.
Aqueous water-absorption preventing agents known thus far include long-lasting emulsions of alkyltrialkoxysilanes emulsified in water as disclosed in Japanese Patent Application Kokai (JP-A) Nos. 292089/1989, 156164/1993, and 221748/1993. These emulsions use alkoxysilanes characterized by very slow hydrolysis reaction. When the emulsions are applied to objective materials, impregnation is effective, but silanes volatilize at the material surface, losing surface water-repellency and allowing water wetting, staining and pop-up due to freezing. Long-lasting action is not expected. Milky white outer appearance is also a problem.
Aside from the emulsion type, a uniform aqueous solution type is disclosed in JP-A 162553/1986 and 249588/1992. These compositions form clear mixtures when diluted with water. When the composition of JP-A 162553/1986 is diluted with water, shelf stability is low in that quick polymerization reaction takes place. It must be used within a day after dilution. This is impractical. The quick polymerization reaction also leads to a higher molecular weight so that material impregnation becomes less efficient, sometimes leaving wetting spots on the material surface.
The composition of JP-A 249588/1992 contains a water-soluble amino-containing coupling agent and an alkyltrialkoxysilane having a short carbon chain. It is shelf stable, but less water repellent because only the lower alkyl group is a water repellent component. The high loading of the amino-containing coupling agent can leave wet color art materials and cause serious yellowing of wood.
Therefore, the above-mentioned water-absorption preventing agents are not considered satisfactory in performance.